They are all related to salary, but have differing meaning.
- 임금 - broad word for wages and salaries of every kind. Used in economics and law.
- 연봉 - annual salary.
- 월급 - monthly salary.
- 급여 - pay, payout, compensation. Often used in accounting as an item of costs.
- 일급 (not 일금) - daily wage.
- 시급, 시간급 - hourly wage.
- 봉급 - salary.
임금 and 급여 are formal and technical sounding words used in official contexts.
봉급 and 월급 are everyday words for salaries from stable jobs For example "I got paid" is said like 나 월급[봉급] 탔다.
연봉 is used when talking about total earnings. 월급 usually doesn't include bonuses and other types of compensation..